Mixamo Import to Unity

Hello!
I am quite a newb when it comes to animations or physics in Unity.
I researched quite a while now and did not come to the desired result.
I am using the Polygon City Character Asset and try to combine this with the animations of Mixamo. Does not work quite well I guess.
I have uploaded my character model and downloaded the animation without sprite, the very first import caused only the arms to be in a wrong angle, way bigger than it should be. So I thought it may be related to the avatar, I changed the avater to force T-Pose and it worked quite well, except for the following symptoms:

The right arm now is sort of stiff, despite everything being equal, the avatar pose, the weight of muscles etc.
Also:

Both legs are bent like this whenever they reach the "maximum" of the movement.
I re-ragdolled four times now in four different varieties, did not help.
I am at the end of my skills and could need some help, would be amazing if you could give me some advice on adjusting the joints (what I also tried without any success).

 

Edit: I updated the Avatar a bit and got to the following:

It looks 100% correct. This however produces two different bugs now, while the legs are totally fine:

This stiff arm is driving me crazy...

 

So I played around and the final result is that the people using the mixamo animation fly and bug through the air.
Any advices?
I checked literally everything I could think of.

 

This is the buggy movement.

 

So these are the exact steps I do.

 

I've also had issues with rotations of arms being wrong, your last video was exactly the issue I had with a Mixamo walking animation. I was using the Standard Assets Unity character and using animations from Mixamo.

What resolved the issue was opening the character in Blender, completely removing the skeleton, and exporting out as FBX. I then imported the character into Mixamo and went through the rigging process. I then download an idle animation with the skin from Mixamo (as FBX for Unity), and imported into Unity as a humanoid. Any more animations I needed from Mixamo I downloaded without the skin. Animations then worked correctly.

I don't have enough knowledge or experience to work out whether this is an issue or just incorrect use. I'm inclined to believe that animations from Mixamo require a specific hierarchy, and by going through it's own rigging process you'll get a rigged humanoid ready for Mixamo animations. But I'm sure someone more experienced can explain.

 

The best way to avoid this kind of problem is downloading from mixamo a character model in t-pose (the same character you used to get animations). And, for all downloaded animations you must set to copy avatar rig from the mixamo model avatar. That will fix this arms and legs distortions, and you can use in your model without problems. If you try to enforce T-pose it will not get a perfect T-pose, and it can mess with your bones rotations.

On the example bellow, I downloaded an animation to be used with unity standard character, but it's using the avatar from mixamo Character.

 

Yeah, I figured that out just yesterday, works now as intended, thank you very much